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VHF Group Bulletin


									The West Australian
VHF Group Bulletin
                                                                    January 2003

                      VH F G R O U
                  N                  P


                                          R P O R AT E


 Calendar                                                Committee
 Jan                    13      VHF Microwave Net        President         Alan    VK6ZWZ
                        20      Committee Meeting        Acting Sec.       Don     VK6HK
                        27      General Meeting          Vice President    Terry   VK6ZLT
 Feb                    10      VHF Microwave Net        Treasurer         Cec     VK6AO
                        17      General Meeting          Activities
                        24      Committee Meeting        Materials
 Mar                    10      VHF Microwave Net        Publicity
                        17      Committee Meeting        Librarian         Al      VK6ZAY
                        24      General Meeting          Museum Rep        Tom     VK6ZAF
 Apr                    13      Field Day                Bulletin Editor   Ben     VK6TLA
                        14      VHF Microwave Net        Councillor        Wally   VK6KZ
                        21      Committee Meeting        Councillor        Terry   VK6TRG
                        28      Annual Gen. Meeting
 May                    12      VHF Microwave Net        The official newsletter for the West Aus-
                        19      Committee Meeting        tralian VHF Group (Inc), PO Box 189 Ap-
                        26      General Meeting          plecross. Email for the editor can be sent
 Jun                     9      VHF Microwave Net
                        16      Committee Meeting
                        23      General Meeting
Editors Notes
Ben Rampling, VK6TLA

       elcome to the January edition of the Bulletin. The change of year brings in a new editor,
W      and a change of typesetting software brings a new design. For those taken by surprise,
I’d better introduce myself. Having been a new and unsuspecting member at the time a new
editor was sought, I volunteered myself with abandon. While I have not held an Amateur
license for any great period, I have clocked up many hours with a soldering iron and bring
previous expertise in publishing.
     The installation of the Mount Barker beacons has been scheduled to take place on or around
24 April. The site lease has recently been taken over by Tim Smith, who has generously donated
the use of the site and his qualifications as a rigger to assist the installation.
      A recent topic of discussion has been the use of GPS as a frequency reference for our
beacons. Don VK6HK has conducted on-air tests with Wal VK6KZ and a 432MHz beacon
transmitter. The resulting carrier accuracy was believed to be better than 5Hz. The transmitter
was modified to run from a DDS signal source, controlled by a GPS disciplined reference.Further
tests are planned on higher bands, and a proposal may be formed to employ a similar system at
selected beacon sites.
     As has been tradition, I am seeking submissions of news items, letters to the editors and
technical articles. We will also be continuing and encouraging the delivery of these bulletins via
Email. If you wish to receive your bulletin by email please contact me.

Eighth WA VHF/UHF/SHF Field Day
Sunday, 13 April, 2003

     1. The contest is open to all individual licensed amateurs. All bands above 50 MHz, and all
licensed modes, may be used.
     2. Points are scored for two way contacts between pairs of stations, at least one of which
must be portable, and at least one of which must be in the VK6 call area. (Repeater contacts
do not count towards the score, but may be used for liaison purposes.) For the purposes of the
contest, a portable station is one which is being operated away from the usual station address and
which is not powered from the AC mains. Mobile stations (including permanently mobile) count
as portable, as does the VHF Group station VK6WH.
     3. CONTEST TIME: 1030-1500 WST (0230Z-0700Z) on Sunday, 13 April, 2003. The
contest is divided into 2 intervals of 2 hours each, 1030-1230 WST and 1300-1500 WST. These
are separated by a half hour (1230-1300 WST) for lunch. Two stations may work each other for
a scoring contact once on each band in each 2 hour interval.
     4. The contest exchange will consist of a signal report, 3 digit serial number starting from
001, and the station location.
     5. Each scoring monoband contact is worth 1 point times the following multipliers:

   One point for each 25km or part thereof, up to a maximum of 15 points.

        Up to (km)          25 50 75 100 125 150 175 200 225 250 275 300 325 350 350+
        Multiplier            1       2   3    4    5    6        7       8    9   10       11   12   13   14    15


          Nom. Freq. MHz       50 144 432 1296 2400 3400 5760 10368 24000 47000 and up
          Multiplier              3       2   3     5        8        8       8         8        12             16

   Contacts count double if both stations are portable, or if one is portable and the other is a country
   fixed station. A country station is one which is at least 100km from GPO Perth.

   Contacts with Limited Novice and Novice stations count quadruple.


                            25 50 75 100 125 150 175 200 225 250 275 300 325 350 350+
        50/432               3        6   9   12   15   18       21   24      27   30       33   36   39   42    45
        144                  2        4   6    8   10   12       14   16      18   20       22   24   26   28    30
        1296                 5 10 15          20   25   30       35   40      45   50       55   60   65   70    75
        2-10GHz              8 16 24          32   40   48       56   64      72   80       88   96 104 112     120
        24GHz               12 24 36          48   60   72       84   96 108 120 132 144 156 168                180
        47GHz & Higher      16 32 48          64   80   96 112 128 144 160 176 192 208 224                      240

     6. SECTIONS: 1. Portable (All band), 2. Portable (Single Band),                                  3. Fixed (All band),
4. Novice.
      All portable contestants should submit with their logs, a tally of their score for each band
(for section 2) and their total score (for section 1).
      7. GROUP OPERATION: There is no section for club stations, but contacts with club
stations count towards the scores of individual amateurs entering sections 1 to 4. Groups of up
to 3 licensed amateurs may pool their equipment, and operate from a single portable site under
their own individual call signs. (An exception is made for VK6WH, which is allowed multiple
operators, and can enter the portable section even if operated from Wireless Hill.) The use of
multiple call signs by a single individual is not allowed.
     8. CROSSBAND CONTACTS are permitted, but only score in special circumstances. If
two stations work crossband from band A to some other band (B, say), but do not have a two way
contact on band A in the relevant 2 hour time period, then once, and only once, in that period,
each may claim towards their band A (and total) score half the points that would have resulted
from a band A contact. This means that if they do not have a two way contact on band B in the
time period, they may also claim (once only) half the points that would have resulted from a band
B contact.
     9. LOGS should be sent by Monday, 28 April, 2003 (April Meeting night) to:


The Contest Manager’s decisions and interpretation of the rules are final.

    REMEMBER: Contacts between a portable station, and a portable or country fixed station,
count double. Contacts with Novice stations count quadruple.
     If things get a bit quiet, some suggested frequencies to try are:

SSB: 50.175, 144.120, 432.120, 1296.120
FM: 52.525, 53.5, 146.5, 439.0, 1296.3
Liaison: 144.175 (SSB), 432.175 (SSB), 145.375 (FM)

APRS Primer
Ben Rampling, VK6TLA

     ARPS, the Automatic Position Reporting System, is a protocol developed by amateurs
to track the location, course, speed and altitude of moving objects. The APRS protocol is
layered over the top of AX.25, and is used in all the same places traditional packet radio can be
found. After years of development and experimentation, it has been extended beyond simple
object tracking, and now supports weather stations, direction finding, fixed station information,
emergency beaconing, short messaging and a generic telemetry format.
      APRS transmitters are often attached to cars, people, boats, remote sites and home stations.
They almost always acquire their location and velocity information from a GPS, however in fixed
stations and all but the most cyclone prone weather stations it is sufficient to use a hardcoded
location and omit the GPS.
      The APRS computer or controller has the task of configuring the GPS on boot, and decoding
the GPS or sensor information. It is rare that much computing power is needed, so when space is
tight a microcontroller can be used. The controller or computers will then encode this data in to
a single APRS packet, and send the packet off to a TNC to be modulated. Some APRS controllers
eliminate the need for a separate TNC by modulating the packet to AFSK, but these controllers
are usually limited to transmit only and fairly simplistic carrier sensing.
           GPS                Computer               TNC                      Radio

Figure 1. A full APRS station. Some stations may use a software TNC, others may use a
transceiver with integrated APRS processing and display.

      An APRS packet is broadcast as single AX.25 frame, in the same way that packet beacons
or packet BBS MAIL notifications are broadcast. The packet will not be acknowledged by any
receiving station, except in some cases where the packet contains a question or short message
for the receiving station. In contrast to typical packet beacons, APRS packets may be digipeated
and will either contain explicit digipeating paths or hints. The hints can specify how far and in
what direction the packet should be retransmitted. Explicit paths can specify particular stations
to digipeat through, but are uncommon due to the mobile nature of most stations.

                                         AX.25 Frame

                       AX.25 Address                            AX.25 Data

              CQ        VK6TLA          RELAY               @          Data

                                           APRS Data

              071306z3150.02N/11610.01W>My APRS Comment

Figure 2. An APRS frame populated with data. The time is 7:13 GMT, and VK6TLA is
somewhere near Perth (31° North, 116° West). Two characters select the icon to display on maps,
the first between the latitude and longitude (/), and the second just between the comment (>).

     So far, we have a way to transmit locations from a moving vehicle. The next problem is
who receives it, and what they do with it. APRS digipeaters extend the propagation of packets in
two ways. Like a voice repeater, an APRS digipeater rebroadcasts any frames heard. All APRS
communications take place on a single channel, and many digipeaters may be in range of the
APRS transmitter. To avert the obvious disaster, digipeaters may use the hints in the APRS frame
to decide if it should repeat the message. Every digipeater will digipeat messages when the next
hop in the path is “RELAY”. A digipeater with extensive coverage of an area will also react to
“WIDE” addresses. A packet jumps through multiple relay or wide digipeaters if the path has
a repeated address. For instance, if you really want to get a message spread far and wide, a path
like “RELAY, RELAY, WIDE, WIDE” will help.
     Another way that APRS stations can propagate packets is via the Internet. An IGATE is
an APRS node that sends packets to a central Internet APRS server to be distributed to all other
APRS IGATE nodes. This allows world wide monitoring of APRS nodes, and short messaging
between any two nodes in the world in range of an IGATE. An easy to use interface to this system
is provided at the web site, and it is also possible to connect APRS software,
usually used to decode on-air packets, to the Internet system.

                           VK6DNE / RELAY

                                               VK6APR / WIDE

Figure 3. A roaming APRS station broadcasts packets in the hope that a nearby digipeater will
receive the packet. In this case, the packet has first been received by a “relay” digipeater and then
by a “wide” digipeater.

      Regardless of how packets reach your station, you’ll want to see what is going on. An APRS
program can be installed on your computer to collect packets on-air, or to connect to an Internet
APRS server. Once your computer is receiving packets, it displays the wandering cars, hikers
or weather stations on a map. Messages can be sent to and from mobile stations, and weather
stations and telemetry beacons can be examined. The software is usually configurable to allow
only local traffic to be viewed, or to zoom out and show (the somewhat crowded) map of nodes
around the country or around the globe.
     It should probably be noted that the above description of APRS glosses over many details of
APRS. The full standard allows for many different message formats and tricks that have appeared
in the rapid evolution of APRS. Full details of APRS, software and the standard can be found at
the web site

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